A power semiconductor is the internal driving force of the continuously developing power-electronic system and has irreplaceable effects, especially in the aspects of energy conservation, dynamic control, noise reduction, etc. The power semiconductor is mainly used for control over the energy transfer between an energy source and a load and has the characteristics of high precision, high speed and low power consumption. In the past 20 years, power device and the encapsulation technology have developed fast, in particular for the power MOS transistors replacing traditional bipolar transistors in many application fields because of the excellent features of high input impedance, short cutoff time, etc. At present, power MOS transistors are mainly classed into the following types: u-shaped MOS transistors (UMOSFET), insulated gate bipolar transistors (IGBT), etc.
The IGBT is a combined, full-control, voltage-drive-type power semiconductor consisting of a bipolar junction transistor (BJT) and a MOS transistor. FIG. 1 shows the structure of an N-trench enhanced IGBT, wherein n-type source regions 104a and 104b are respectively formed in the p-type regions (sub-trench regions) 103a and 103b, a gate stack region 110 is comprised of a gate dielectric layer 105 and a gate electrode 106, the gate dielectric layer 105 may be silicon dioxide, and the gate electrode 106 may be doped polycrystalline. The working trench region of the device is formed on the surface of the substrate close to the gate stack region 110. An n-type drift region 102 is formed above an n-type drain region 101; a P+ region 100 on the other side of the drain region 101 is a drain injection region which is an exclusive functional region of the IGBT, which together with the drain region and the sub-trench region forms a PNP bipolar transistor to function as an emitter, injecting hollow cavities into the drain region and performing conducive modulation to reduce the conductive voltage of the device. The switching function of the IGBT refers to an applied positive gate voltage to form trenches and provide a base current to the PNP transistor so as to turn the IGBT on, or on the contrary, apply a negative gate electrode to remove the trenches and cut off the base current so as to turn the IGBT off. The IGBT has the combined advantages of high input impedance of the MOSFET and low conductive voltage drop of the gate turn-off transistor (GTR) and is therefore very suitable for application in DC systems with a DC voltage of 600V or above, such as DC motors, frequency converters, switching power supplies, illumination circuits, traction drives, etc.
At present, mainstream IGBT need high-priced floating zone silicon as the substrate. Furthermore, if the IGBT is manufactured by the prior art, back ion implantation and low-temperature annealing processes which are susceptible to damaging the front metal are required; meanwhile, the back surface needs thinning, which is complicated and easily damages the silicon wafer.